1. Field of the Invention
The present invention is directed to a pressure pulse source for generating acoustic pressure pulses in an acoustic propagation medium, and in particular to a pressure pulse source operating according to the traveling wave principle.
2. Description of the Prior Art
Pressure pulse sources can be employed, for example, in medicine for the disintegration of calculi (lithotripsy), for treating tumors and for treating bone pathologies (osteorestoration). Such pressure pulse sources can also be used for non-medical purposes, for example in materials testing. For all uses, the pressure source must be acoustically coupled to the subject to be acoustically irradiated in a suitable manner, in order to ensure a low-loss introduction of the pressure pulses into the subject. The pressure pulse source and the subject must also be aligned relative to each other so that the region of the subject which is to be acoustically irradiated is located in the propagation path of the pressure pulses, or is located in the focal zone of the pressure pulses in the case of focused pressure pulses.
A pressure pulse source for medical purposes operating according to the traveling wave principle is described in German OS 38 17 996. In this pressure pulse source, a plurality of foils are disposed spaced from each other by a defined acoustic propagation path in a liquid acoustic propagation medium disposed between each of the foils. The foils are driven according to the traveling wave principle, which is understood in the art and is used herein to mean that the foil farthest from the acoustic propagation medium is first, separately driven to generate a pressure pulse, and the foil immediately following in the propagation direction of the pressure pulse is then separately driven for generating a pressure pulse when the pressure pulse generated by the first-driven foil reaches that foil, and so on until all of the foils have been driven in succession. This results in a superimposition of the pressure pulses generated by the individual foils, so that the peak amplitude of the wavefront, and thus the pressure associated therewith, is continuously increased.
In the aforementioned German OS 38 17 996, the spacing of the foils, separated by a defined liquid propagation path, is intended to prevent the foils from mutually influencing each other in terms of their frequency behavior. It has been shown that this known pressure pulse source is fundamentally functional, but the pressure magnitude obtainable, even with the use of a large number of foils, is rather low in comparison to known electro-hydraulic sources (of the type described in German OS 23 51 247), known electromagnetic sources (of the type described in European Application 0 188 750, corresponding to U.S. Pat. No. 4,697,588) and piezoelectric pressure pulse sources (of the type described in German OS 34 25 992), which are not operated according to the traveling wave principle.
As is understood by those skilled in the art, and as used herein, the term "foil" means a planar structure having a thickness which does not exceed a few millimeters.